Closely related to armadillos and anteaters, sloths originated in South America in the Late Eocene period, the "dawn of recent life," when South America became "became home to a unique zoo of hoofed mammals, edentates, marsupials, and more giant flightless birds (Phorusrachids)." There were at one time over 35 types of sloths, ranging from Antartica up through Central America. Now there are only two with five species living in the tropical rain forests of Central and South America.
There are two species of two-toed sloth in South America (Choloepus hoffmanni or Unau) found in the forested regions of northern South America from Ecuador to Costa Rica, and (Choloepus didattylus) in Brazil. There are three species of three-toed sloth (Bradypus variegatus) in in coastal Ecuador, through Columbia and Venezuela (except for Llanos, and the Orinoco river delta), continuing through the forested areas of Ecuador, Peru, Bolivia, through-out Brazil and extending to the northern portion of Argentina and Central America,
The difference between the species, as named, is in the front toes, as both genera have three toes on their hind feet, but they are not related families.
The worlds slowest moving mammal, sloths are tree dwellers, safer from ground predators. They carry out most of their activities hanging upside down in trees. They eat, sleep, mate, give birth, and tend their young suspended over the ground. It takes them about two and half years to grow to full size, between one and a half and two and a half feet. (Their ancestor, the extinct Giant Sloth, grew to the size of an elephant.) They may live for forty years.
Due to this upside down life, their internal organs are in different positions.
Sloths are very slow on the ground, moving only about 53 feet per hour. Faster in the trees, they can move about 480 feet/hour, and in cases of emergency have been tracked moving at 900 feet/hour.
Sloths prefer a slow paced way of life. They spend most of the day resting and sleeping. At night, they eat, descend to the ground only to move to another location or to defecate, usually once weekly.
Sloths are herbivores and eat tree leaves, shoots and some fruit. The two-toed species also eat twigs, fruits, and small prey. Their digestive systems are very slow, due to their leisurely metabolic systems, allowing them to survive on little food intake. They get their water from dewdrops or the juice in the leaves. This low rate of metabolism makes it hard for them to fight off illness or colder climates.
They have long, curved claws which allow them to grip a tree branch and hang on even while sleeping. They use their lips, which are very hard, to crop the leaves. Continually growing and self-sharpening, their teeth grind their food. They may use their teeth to nip at a predator.
Sloths use their long, thick gray or brown hair, usually covered with blue-green algae during the rainy season, as protective coloration. Their hair covers them from stomach to back, falling over them as they hang suspended.
Predators include large snakes, harpy and other birds, jaguars and ocelots.
Sloths have short flat heads, short snouts and tiny ears. See these photos. Besides the number of forefeet toes, there are these differences between two-toed and three-toed sloths:
With the steady encroachment by man and machine into the rain forests of South America, the sloths, like many other tropical rain forest creatures, are in danger.